PROJECT ABSTRACT Food allergy often starts early in life and can be life threatening. Early introduction of peanut consumption is recommended to reduce development of peanut allergy. However, in the LEAP study, 14% of children were not included because they were skin prick positive for peanut allergy at the start or because they developed reactions during oral peanut exposures. Peanut allergy is associated with loss-of-function mutations in skin barrier genes. In mechanistic studies, we demonstrated that neonatal mice with heterozygous skin barrier mutations developed food allergy by skin co-exposure to detergent, food allergen and a ubiquitous environmental allergen, Alternaria alternata (Alt) or house dust mite extract. Importantly, the skin sensitizations were performed before any visual evidence of eczema in the neonates. It is conceivable that for children, skin sensitization with food antigens could occur before clinical signs of eczema. We demonstrated that oral peanut consumption before skin sensitization inhibited development of food allergy, but this inhibition was blocked by Alt on the skin during oral peanut consumption. This may be important for children with skin barrier defects but without early signs of eczema, who are exposed to ubiquitous environmental allergens while undergoing oral peanut induction of tolerance. In this proposal, we develop the novel concept that there are skin-derived systemic factors that block tolerance and that can serve as risk factors for development of food allergy, and that, there are skin-derived factors that may predict existence of sensitization to food allergy before oral consumption of food allergens. Our preliminary data from bulk and single cell RNA-seq analyses of sensitized skin from neonatal mice indicate signals that define unique function of environmental allergen for induction of food allergy and signals that are unique to the combination of Alt and food allergen exposure of neonates with skin barrier mutations. Our long-term goal is to identify mechanisms for initiation of food allergy by skin exposures and identify factors for detection of risk for skin sensitization. As a step towards our long-term goal, our central HYPOTHESIS is that initiation of food allergy by skin exposure to allergen is mediated by signals from skin with barrier mutations that induce a network of cell signals for activation of the immune system to generate allergen-specific IgE. We will test our central hypothesis with the following aims: Aim 1. Test the hypotheses that skin, with barrier mutations, stimulated by food allergens and environmental allergens produce factors that A) are systemic signals, B) can block oral food antigen-induced tolerance and C) can mediate susceptibility to development of food allergy. Aim 2. Test the hypothesis that initiation of food allergy is mediated by recognition molecules expressed by skin with barrier mutations. Aim 3. Test the hypothesis that allergen stimulates keratinocytes with defects in skin barrier genes (Flg or Tmem79) via pathways that converge to induce expression of a common set of factors detected in the RNA-seq analysis.